There is a continuing need for apparatus for drilling holes into the ground. Holes are required for wells, and fence posts must be secured in the ground. Shafts are required for placing explosives deep into the ground for seismological testing purposes. Piles need to be driven into the ground for building various structures, and tubes must be placed in the ground to monitor groundwater. Large diameter soil samples are required for engineering, environmental, agricultural and mining purposes.
Drill stands have been used for many years for these purposes. Most drill stands use a rotational drilling technique to allow the drill shaft to penetrate the soil. However, in recent years vibratory drills have gained favour for many of these same applications.
The use of high frequency vibratory drills facilitates the collection of sediment cores with minimal disruption of the circumference layer and without serious compaction and dewatering of the sample. U.S. Pat. No. 5,004,055 to Porritt et. al. discloses a drill core apparatus comprising a sampler tube, a drill stand and a vibratory head for the sampler tube. The vibratory head comprises a pair of eccentric cams mounted on a shaft at a variable angle to one another within a housing. The drive is powered by a hydraulic drive motor. The amplitude of vibration is adjusted by changing the angle between the cams.
The above vibratory drill head above has proven to be very successful. However, in certain situations greater vibratory force is required than can be applied using this drill head. As well, with the greater vibratory force it is desirable that horizontal vibration be reduced.